Effects of cytokines, growth factors, extracellular matrix proteins and recent evidence of viral proteins on pluripotent stem cell differentiation has led the applicant to hypothesize that viral Tat and/or Nef proteins may affect the overall proliferation and differentiation of the hematopoietic progenitor cells via alteration of production of the various cytokines in the stromal cells and/or induction of a direct inhibitory effect on the CD34+ cells. To test this hypothesis, the P.I. proposes to investigate the effects of Tat and/or Nef proteins, either directly or by the co-culture techniques utilizing the HeLa-tat and/or HeLa-nef stably transfected cell lines on the primary CD34+ cells, the stromal cells and the transformed progenitor cells, K562 and HL-60. Specifically, following aims will be investigated: (1) proliferation and differentiation of CD34+ cells, and K-562 and HL-60 cells in the presence and absence of stromal cells both untreated and pretreated with the viral proteins; (2) the effect of the viral proteins on signal transduction pathways; (3) the levels of cytokines released by the stromal cells and monitoring of the corresponding mRNA levels; (4) the expression of protooncogenes and of the cell surface receptors; (5) the modulation of the function of various transcription factors via direct protein-protein interactions; and (6) the mechanisms that may be responsible for the viral protein-induced modulation of apoptotic pathways in the progenitor cells. The applicant believes that the proposed experiments will provide an in-depth understanding of the mechanisms that may be involved in HIV-induced hematopoietic suppression.